In recent years, there have been proposed and developed various variable valve operating devices capable of variably controlling an engine valve lift characteristic. Such variable valve operating devices have been disclosed in (i) International Publication No. WO 02/092972 corresponding to U.S. Pat. No. 6,907,852, and also corresponding to Japanese Patent Provisional Publication No. 2004-521234 (hereinafter is referred to as “JP2004-521234”), and (ii) Japanese Patent Provisional Publication No. 2005-009330 (hereinafter is referred to as “JP2005-009330”).
In the variable valve operating device disclosed in JP2004-521234 (WO 02/092972), a drive cam fixed to a camshaft creates oscillating motion of a spring-loaded pivoting lever (a valve actuation member). The oscillating motion of the pivoting lever is transmitted via a swing arm (a motion-transmission element or a motion-transfer element) to the valve stem end of an intake valve, so as to open and close the intake valve. Also provided is a curved disc-shaped member, serving as an eccentric cam and constructing part of a variable valve-lift adjustment mechanism (simply, a variable valve lift mechanism). The curved disc-shaped member (eccentric cam) is rotatable about its rotation center, while being kept in abutted-engagement with the pivoting lever. Rotary motion of the eccentric cam changes the fulcrum of oscillating motion of the pivoting lever, thereby enabling variable control of the valve lift characteristic of the intake valve.
On the other hand, the variable valve operating device disclosed in JP2005-009330 assigned to the assignee of the present invention, is comprised of a drive shaft formed on its outer periphery with a drive eccentric-cam, a rockable cam fixed to a cylindrical camshaft, which camshaft is rotatably supported on the outer periphery of the drive shaft so as to open and close an intake valve by way of rockable motion of the rockable cam, a rocker arm rotatably linked at one end to the drive eccentric-cam via a link arm and rotatably linked at the other end to the rockable cam via a link rod, and a control cam fixed to a control shaft extending in the longitudinal direction of the engine, for changing the fulcrum of oscillating motion of the rocker arm. Concretely, the fulcrum of oscillating motion of the rocker arm is changed by rotating the control cam to a desired angular position via the control shaft by means of an actuator, depending on an engine operating condition. Changing the fulcrum of oscillating motion of the rocker arm results in a change in an engine valve lift characteristic.